Cooling System - Corrosion
86porsche03Subject: Corrosion in the Cooling System
Model
All Water
Cooled
Group
1
Part Identifier
19--
Number
8629
Dec. 16, 1986
Corrosion could occur in the coolant pipes or cooling system as a result of:
- long down-time or storage of the vehicles.
- a coolant and antifreeze mixture which is older than 2 years.
- an antifreeze concentration of less than 30%.
- dirt in the cooling system (corrosion dirt).
Porsche recommends phosphate-free coolant, which has additives to prevent corrosion in the cooling system in addition to the glycol. Some of these additives, however, do not have sufficient aging stability.
Oxygen:
Glycol reacts with oxygen to form acid. Oxygen enters the cooling system via the seals. Cold coolant takes on more oxygen than warm coolant.
This results in:
- a lower content of glycol in the coolant and
- the antifreeze safety temperature rising in direction of 0~C (32~F).
Reserve Alkalinity:
This is defined as the alkaline additives which bind (neutralize) the produced acids. The acid volume increases when these additives are used up. The coolant then becomes more aggressive, resulting in accelerated corrosion.
Corrosion Dirt:
The corrosion dirt circulated in the coolant circuit will rub freshly protective coats off the inside of the cooling system components. The protective coat must then be built up from new, resulting in faster consumption of these protective additives (e.g. silicate for aluminum).
Antifreeze Content:
It should be at least 30% and not more than 55% (check manufacturer's recommendations).
Content less than 30%:
- the corrosion inhibitors cannot produce a complete protective coat which will result in local corrosion.
Content more than 55%:
- the heat conductivity of the coolant is lower, therefore, higher coolant temperature results.
- corrosion inhibition is impaired since the inhibitors are only effective with a sufficient water content.
Note the following (points) in case of opened cans or containers of antifreeze:
1. The cans or containers must be closed (caps, covers) after using.
2. The date of the initial opening should be noted on the cans or containers.
3. The remaining antifreeze must be used up within six to nine months.